To determine whether the impairment in renal calcium conservation is due to age-related factors other than estrogen deficiency, or to estrogen deficiency; and to determine if this abnormality is due to an impairment in PTH-mediated renal calcium transport. In a further extension of our earlier protocol (5B94), where we looked at decreased tubular reabsorption of calcium in osteoporosis, we now are studying the effect of aging and estrogen in a normal population. At this time we are in the process of completing the analysis and have no further plans to continue until we have had a chance to review the data.